Mercury switch relay and circuit



July 15, 19407 U. c. Hr-:DIN E-r AL 2,208,271

MERCURY SWITCH RELAY AND CIRCUIT Filed Feb. 2 4, 1937 5 Sheets-Sheet 1 gfm' ELU/QJ( fors lUzo C. ff@ dj/L July16,1940 U..HED|N E-FAL 2,208,211

MERCURY SWITCH RELAY AND CIRCUIT Filed Feb. 24, 1957 3 Sheets-Sheet 2 .E1/@www5 [fno 8.1766221?, Ca/* H Za/2607@ @www m A"illy 15, 1940- U. c. HEDIN Er AL 2,208,271

MERCURY SWITCH RELAY AND CIRCUIT Filed Feb. 24, 1957 3 Sheets-Sheet 5 www Patented July 16, 1940 PATENT Fries manchar swiron RELAY AND elacnr'r lino C. lriedin and Carl H. lLarson, Elkhart, ind.,

assignors to Elhe Adlake Company, a corporation oi illinois Application February 24, i937, Serial No. 127,390

it? Claims.

It is common practice to control a load relay by means of a pilot relay, but ordinarily the operating coil for the load switch is energized from a dilerent source than that used by the pilot s relay.

in most mercury switch relays, and to some extent, in electromechanical relays, the span between the pickup and drop away values of the relay is directly proportional (as distinguished 1o from inversely proportional) to the load carried by the relay, i. e. if the relay is to handle a heavy load, it is very diiiicult, if not impossible, to obtain a small span betweenthe pickup and drop away values of the relay, yet many times this l relationship between load and voltage span is highly desirable.

It is one of the objects of this invention to provide means for operating a heavy load relay on small differences of voltage.

The relay and circuit of this invention also has another important application and use, and that is in cases where it is desirable to have the condition of the circuit controlled by the load switch changed only after there has been a continuous, as distinguished from a momentary,

change in the voltage of the control circuit.

These and other objects and advantages will become apparent as the disclosure proceeds and the description is read in conjunction with the accompanying semi-diagrammatic drawings, ln

which Fig. l shows a relay which is adapted to change the condition of a load circuit only after the control circuit has dropped below a predetermined minimum voltage for a specified length of time, the load switch being shown in its open circuit position;

Fig. 2 is a view oi the relay shown in Fig. l with the load switch in its closed circuit position; l

Fig. 3 is a view of a relay which is used for heavy loads;

Fig. 4 is a view showing a relay in which the load switch has a time delay element which acts both upon opening and closing of the associated electrical circuit; l

Fig. 5 is a diagram in which the voltage of the control circuit is plotted against time; and

Fig. 6 shows a modied form of the invention.

53 The illustrative embodiments of the invention shown in the drawingsand hereafter described are chosen for the purpose of complying with Sec. 4888 of the Revised Statutes, but the appended claims should be construed as broadly as the 55 prior art will permit.

(Cl. 17d-320) The relay shown in Figs. l and 2 is used where an electrical` circuit is to be closed whenever the circuit to be controlled 'alls below a predetermined voltage for a speciiied length of time. The relay is particularly useful in cases where g the control or primary circuit is subject to comparatively gradual rises and falls in potential, or where that circuit is likely to fluctuate between rather narrow limits o voltage near the critical voltage of the relay. It is not desirable To to close the load or secondary circuit unless the primary circuit has deiinitely fallen below a predetermined minimum value for a denite period of time and the relay of Figs. 1 and 2 is intended to accomplish this object. le

The load switch is indicated at l@ and the control switch at il, the former being of the mercury displacement type disclosed in Larson 1,967,946, and the latter being of the mercury displacement type disclosed in Larson Patent 20 No. 1,967,247. The load switch is a slow make, quick break switch, i. e. the circuit which it controls is not closed until a predetermined length of time has elapsed after the operating coil has been de-energized, whereas the circuit is opened 25 immediately whenever the associated operating coil is energized. The control switch Il is of the fast acting type, i. e. it has no time delay element to introduce a lag between the operation of the associated operating coil and the circuit e@ which the switch controls.

The control switch ll is operated by a coil l2 and comprises brieily a switch envelope i3 through the base of which electrodes i4 and l5 are suitably sealed, the former being insulated to a point adjacent to its top by a sleeve I6 with the bared end ll of the electrode bent over to form a suitable contact surface. The switch envelope has a mercury fill I8, the level of which is changed by a magnetically responsive displacer i9 operating under the influence of the coil l2. The displacer is guided in its movement by suitable guides 20, and springs 2| at the top and bottom of the displacer protect the ends of the switch envelope against breakage.

Magnetic pole sleeves 22 telescoped over -the switch envelope I3 fix the position of the air gap 23 which influences the movement of the displacer I9.

The load switch IIJ comprises a switch envelope 25 through the base of which electrodes 26 and 2l are sealed, the former having an insulating sleeve 28 surrounding it for a portion of .its height, leaving the upper part of the electrode 26 bare, as indicated at 29. A thimble 30 u the bared end 29 of the electrode 26 with itslower edge 3 extending below the top 32 of the insulating sleeve 28.

A magnetically responsive displacer generally indicated at 33 is normally held in suspended position by an operating coil 34, the air gap for the iron circuit associated with the coil being indicated at 35. The displacer in this case consists of an outer shell 36 of magnetic material and an inner tube 31 of glass or ceramic material, the former seating upon a ledge 38 formed on the tube 31, and the two being frlctionally held together by a spring 39 telescoped over the projecting end of the glass tube 31. 'I'he bottom end of the tube 31 projects downwardly over the thimble 30, the latter constituting the time delay element of the switch. When the coil 34 is de- 'energ'ized, the displacer 33 is releasedfrom its suspended positionv and displaces ae suicient quantity of mercury to raise the outside mercury level above the top 32 of the sleeve 28, but the mercury level within the thimble 3U rises at a rate which corresponds to the seepage of the entrapped gas within the thimble through the pores of the wall. After a predetermined period of time has elapsed subsequent to the releasing of the displacer from its suspended position, the mercury level within the th1mble'3ll will rise above the top 32 of the insulating sleeve 28, thereby closing the circuit between the electrodes 26 and 21, and this time interval is the same for every lowering of the displacer 33 providing the latter always starts from its original suspended position.

The closed circuit position of the load switch is shown in Fig. 2 with the tube 31 resting upon a spring 30,' frictionally secured to the insulating sleeve 28 associated with' the central electrode 26, and when the coil 34 is again energized, the

displacer 33 is lifted by magnetic force to the' position shown in Fig. 1 with the result that the mercury level immediately falls to the position in which it is shown in Fig. l, thereby breaking the electrical circuit between the electrodes 25 and 21 without delay.v The switch, therefore, operates as a slow make, quick break switch.

Let it be assumed that the entire relay, which for convenience will be designated generally til, is to close a secondary circuit, generally designated d2, whenever the primary circuit generally designated 43 falls below a predetermined standard for a period of time'corresponding to the time delay action of the thimble 36 of the load switch Ill. The load or secondary circuit may include a sour'ce of electromotive force 'lll'and a relay 35 which may be used to ring an alarm or energize other relays for connecting the load d6 of the primary circuit to some other source of electromotive force.

The load 83 of the primary circuit is shown connected across the secondary of a transformer lil which may be considered as the source of electromotive force for the primary circuit. The operating coil I 2 of the control switch andthe `\,operating coil 3d of the. load switch are likewise connected across the secondary of the transformer 31, but the latter coil is connected in series with lcontacts I@ and I5 of the control switch 'so that its action is dependent upon the -icontrol switch.

It will be convenient to 'illustrate the action ofthe relay 3l by g deiinite voltage conditions in the source 41 of the electromotive force and assigning suitable pickup and drop away values, all of which are capable of being obtained, to the load and control switches I8 and I2. For example, let it be assumed that the source 41 is normally 220 volts, and that the secondary circuit V42 is to be energized whenever the. voltage of the source falls below 180 volts for a period of say three seconds; also that the secondary circuit is to be de-energized whenever the source 41 is restored to 190 volts or higher. Under suchcircumstances, the control switch coil I2 will be wound so that the control relay represented by the switch II and coil I2 will have a drop away value of 180 volts and a pickup value of 190 volts. ,The load switch relay represented by the coil 34 and the switch Ill should then'have a somewhat lower range of pickup and drop away values, for example, a drop away of volts and apickup of 140 volts, and the time delay element of the load switch Il) should have a time factor of three seconds. y

If now the source gradually falls in potential below volts, the coil 34 of the load relay will Vbe de-energized at the instant when the control switch II opens the circuit between the electrodes I4 and I5, i. e., when the voltage drops below 180 volts. As soon as the coil 34 is deenergized, the displacer '33 falls to the position shown in Fig. 2 and the mercury level will start to rise in the thimble 30 to close the circuit through the electrodes 26 and 21 after a three second interval. Should the voltage of the source 41 be restored to normal within that period, or atleast rise above volts, the coil 35 will again be energized) and the mercury will fall away vfrom the thimble 30 before it has had an opportunity to reach the bared end 29 of the electrode 26. It is, therefore, obvious that in the arrangementshown in Figs.V 1 and 2, the voltage in the source A41 must drop below 180 volts for a period of at least three -seconds (for the conditions assumed) before the secondary circuit i2 is closed through the electrodes 26 and 21.

If a control switch II had not been used, and the load switch i0 had been directly responsive to the voltage condition of the source 41, the

gradual fall in potential would have resulted in age had reached a critical value of the relay.

Upon reaching this value, the displacer 33 would fall to the position shown in Fig. 2, but the secondary circuit i2 would be closed within a shorter interval Vthan three seconds because of the mercury that had entered the thimble 30 before the voltage had fallen to the drop away of 'the relay. Obviously this ls an undesirable condition which the circuit arrangement and relays of this invention overcome.

vrr1`he control relay also tends to prevent uctuations of voltage near the critical drop away value of the relay from operating the aload switch lo for ifthe load relay were to be used alone, a momentary drop in voltage would drop the displacer of the load switch and start the time interval running for closing the secondary circuit, even though the primary circuit immediately returned to a voltage above the drop away value of the relay, but below the pickup value of the relay. Furthermore, it would be very diiiicult, if not impossibleyto have a switch of the' type shown in Fig. 2 operatejon a ten volt diierence between aaoaan pickup and drop away values/for a source normally operating at 220 volts/r In Fig. 3, the control/switch II is identical with the corresponding switch in Figs. l and 2, and its operating coil Iii/'is similarly connected across the source 41. The same reference characters will, therefore, be used for corresponding parts.

'I'ne load switch 50 in this case is a fast acting. heavy duty switch adapted to control a high amperage load represented by lamps 5I.. The switch comprises a switch envelope 52 through the base of which electrodes 53A and 54 are suitably sealed, the former being enclosed within a tube 55 of insulating material, preferably of glass, to the top of which a tube 56 of ceramic material is fused, or otherwise secured. The mercury fill 51 of the switch occupies the space within the coaxial tubes 55 and 56, as well as the space outside, and the mercury level is shifted by a displacer 58 in response to'a coil 59 to make or break a circuit through the electrodes 53 and 54, according to the condition oi' the coil 59. The switch 50 is commonly known as a fast acting mercury to mercury contact heavy duty circuit breaker.

A mercury to mercury circuit breaker of this type necessarily requires a rather wide span between pickup and drop away values for operation and yet there are circuits in which condition necessitatecloser regulation.

A switch of the type indicated at II is capable of operating on small differences between pickup and drop away values so that by using the switch I I as a control for the operating coil 59 of the load switch as shown in Fig. 3, theL load switch is actually operated on much smaller changes in voltage than would otherwise' be possible. To do this, however, 'the operating coil I2 for the control switch should be wound to provide the desired pickup and drop away values of the entire relay and for illustration, it may be assumed that the circuit through the` electrodes I4 and I5 'of the control switch should be closed whenever the voltage in the source 41 is 190 volts or more, and should be open whenver the source of voltage is 180 volts or less. For `these values, the coil 5S may be wound so that it will pickup at 140 volts and drop away at 95 volts. l

The reason for having the load relay operate on substantially lower pickup and drop away voltages than areused for the control relay is because thisrelationship between the operating characteristics of the two relays makes certain (with a relatively large factor of safety) that whenever the control relay drops away, the load control relay picks up, thev load relay will likewise pick up.

It will be understood, however,1 that the relationship between the operating characteristics of the two relays may vary within rather wide limits.

The relay and circuit combination shown in Fig. 4 is similar to the one "shown in Figs. l and 2, the principal `difference being. that the load switch 60 is a slow-make, slow-break front contact switch instead of a slow-make, quick-break back contact switch. The relay and circuit'ar-4 rangement isl advantageously-used for controlling the operation of a motor running under a heavy load/ since it is desirable to shut oil the motor whenever the voltage falls below a predetermined standard, say 180 volts, for a specied period, for example, three seconds, and for the motor to be turned on again whenever the voltage is restored to some higher value, say 190 volts, for a specified period, for example three seconds.

The control switch II has its contacts I4 and I5 connected to the operating coil 6I of the load switch 60 as in Figs. l, 2 and 3, and both of the operating coils for the switches II and 60 are connected across the secondary of the source 41. The load, which in this case is a motor, is indicated at 62 and it also is connected across the secondary of the source 41 but in series with contacts 63 and 54 sealed through the base of the switch envelope 65 of the switch 60.

The ceramic thimble 66 which caps the bared end 61 of the central electrode 63 is similar in all respects to the thimble 30 shown in Figs. 1 and 2 with the exception that its lower margin 68 is substantially below the top 69 of the insulating sleeve III surrounding the central electrode and isalso substantially below the normal level oi the mercury indicated at 1I (i. e. the level of the mercury when the coil 6I is deenergized and the mercury is at equilibrium). By this proportioning of the parts, a time delay is introduced into l both the closing and opening of the electrical circuit through the electrodes 63 and 64, since the displacer 12 v,fnever lowers the mercury level sufficiently to allow the outside mercury level to fall below the bottom 68 of the thimble 66, and, consequ'ently, the energization and de-energization of the coil 6I merely establishes a difference of mercury level within and outside of the thimble 66, after which, equilibrium can be established only by the lretarded flow of gas through the pores of the thimble 66.

By properly locating the top 69 of the insulatregualting the stroke of the displacer 12 (which Aing sleeve 1li), the normal mercury level 1I- and I the lowervmargin 68 of the thimble 66 and byy can be done by varying the air gap in the magof 190 volts and a drop-away value of 180 volts` and the load relay may have a pickup value of- Volts and a drop-away value of 110'volts. If.now. the voltage of the source falls from its normal of 220 volts to below volts, the circuit through the electrodes I4 and I5 will be opened causing the coil 6I of the load relay to become de-energized. As soon as this occurs, the displacer 12 rises by,its buoyancy, causing the outside mercury level to fall to a position such as indicated by the line 13. The inside mercury v level, i. e., the level within the thimble 66, will gradually recedethe decline being determined bypthe 4porosity of the thimble 66. After a predetermined interval, which, for the purpose of illustration, may be three seconds, the circuit g5 mined period of time has elapsed to permit the Vmercury within the thimble C6 to rise from the level indicated at il to the top of the insulating sleeve 1U. When this happens, the circuit through the motor 62 is again .closed.

The advantage of having a time delay between the restoration of the voltage of the source and the starting of the motor is to allow the voltage in the source to become more or less constant in value and to allow the wlld iiurituations, which often occur upon restoration oi voltage, to level oi.

The relay and circuit of Fig. 6 combine the advantges of the time delay load switch of Figs. l and 2 with the heavy duty load switch of Fig. 3. The control relay il is identical with the one shown in Figs.' 1 and 2 and the load switch t@ is identical with the load switch of Fig. 3. The intermediate switch l5 is identical. with the load switch @il of Fig. d with'the exception that the bottom edge it of the time delay element d is slightly above'the mercury level when the relay is de-energized, so that theswitch operates as a slow make, quick break front contact switch.

The circuit employed in Fig. 6 for the purpose of illustration is similar to that ofFigs. 1 and 2, the intermediate or dampening switch I5 having its coil 60 connected across. the transformer 41 in .series with the electrodes'of the control switch -ll andthe operating coil 59 of the load switch being likewise connected across the transformer 41, but in series with the electrodes of the dampening switch 15.

If desired,A the dampening switch may be madel to provide a time interval both when the control relay il picks up and drops away and in such 'a' case, the time delay element 86 would be extended further into the mercury inthe manner shown in Fig. 4. vIn this case, the load circuit of Fig. 4 may be used in place of the independent load circuit indicated by t2 (Figs. l. 2 and 6).

Throughout this specication, it has been convenient to use such expressions as` voltage dropping below 180 volts for a given period oi time" and voltage rising above 190 volts for a given period of time, but it should be understood that while the voltage changes in the control circuit will ordinarily respond literally to the language quoted above, there are some types of uctuation in the control. circuit which will cause the load relay to operate even though the voltage in the control circuit-is not maintained for a speciiied period above or below the value which initially causes operation of the control relay. Forexample. the voltage iluctuation'oi the control oircuit indicated by the portion A o! the curve in Fig. 5 illustrates the situation in which a mo.

mentary drop oi the control circuit voltage below 180 volts causes the load relays ot 1, 2 and 4 to become. de-energized but the lload relays cannot again pickup because the voltage,

while it rises above 180 volts. does not reach the. pickup value or 190 volts of the control relay until after say 9 seconds'have elapsed, and within this period, the three second time delay oi the load switches .has allowed the load circuits to be completed) Figs. 1, 2 and 4).

A. similar situation occurs whenv the control.

` circuit voltage surges ,momentarily above 190 volts after having been below that value and' then continues to uctuate between 190 and '180 volts for a period longer than the time delay provided in the load switches. This situation is illustrated by the portion B of the curve in' Fig. 5 and the aotionrof the load relay in Fig. 4, for once the control relay has picked up. the time delay eleaaoaavi ment o! the load switch will permit the closing of the load circuit after a predetermined time interval has elapsed, unless the control .relay again drops awaywithin that period of time.

The portion oi.' the curve in Fig. 5 indicated by C shows a type of voltage uctuation which the control relay eectively handles without causing operation of the load switches of Figs. 1, 2, 4 and 6.

The portion D oi .the curve ineFig. 5 indicates the manner in which a gradual fall in voltage immediately prior to the dropping away of the control relay will eect an accurate timing of the closing of the load circuit whereas such a result could not be obtained if the voltage were applied directly to the coil of the load switch. Y

Because of the situations illustrated by A and B on the curve of Fig. 5, it isobvious that the relay and circuit of this invention give more accurate regulation 'than could be obtained without the use of a pilot relay, for the greater the span between the pickup and drop away values of the relay, the more aggravated is the inaccuracy' caused by the voltage conditions represented by A and B in Fig. 5.

' In all forms of the invention,the action of the load switch is characterized by positive on" or oi action as distinguished from the action of a control switch in which the position of the displacer is substantially proportional to the voltage in the operating coil, or, stated in other words, the relatively low pickup and drop-away values of the load relay make the relay insensitive to iiuctuations in line voltage other than those which are suflciently sustained to make positive operation of the load relay desirable.

All speciiic voltage and timedelay values reierred to herein are merely illustrative', and do not impose limitations on the appended claims.

We claim:

vsaid source for operating the load switch, a control switch having its contacts in series with the coil of the load switch and an operating coil for the control switch connected to said source.

2. In combination, a source of electromotive 1. In combination, a source of electromotive i.

force that is 'subject to comparatively gradualV rises and falls in potential and/or rapid iuctuations of voltage within rather narrow ranges of potentials, a' mercury' switch relay connected to said source and adapted to close an electrical eircuit whenever the source of electromotive force has fallen below a specied value for a predetermined period of4 time, said relay comprising a load switch of the back contact `time delay mercury displacement type, a coil connected to 'said source for operating the load switch, a e'ontrol switch having its contacts in series with the coil oi' the load switch and connected to said source,'and an operating coil for the control switch connected to said source, the pickup and drop away values of the load switch coil being f yless thanthe "correspondingl values for -thecontrol switch coil.

3. In combination, a source otrelectronlotivo l force, a relay for changingthe condition of an electrical circuit whenever the' source has fallen below a specified voltage for a predetermined length of time, said relay including a load switch having a time delay element, a coil for operating the load switch. a control switch having itscontacts connected in series with the load switch coil and the source, and an operating coil forL thel control switch also connected to the source, said series connection operating to continuously maintain the load switch in its desired position until the source has fallen below said specified voltage for said specified period of time, and then return the load switch ,o said position whenever the voltage rises above said specirfled voltage.

4. In combination, a source of electromotive force, a relay for changing the condition oi an electrical circuit after the source potential has varied by some given amount, said relay including a load switch having an operating coil, a control switch having its contacts connected in series with the coil of thefload switch and` the source, and an operating coil i'or the control switch also connected to said source, said series connection operating to continuously maintain thel load switch in its desired position until the source has varied by said given amount and then return the load switch to said position whenever the voltage returns to its normal value.

5. In combination, a source of electromotive force. a relay for changing the condition of an electrical circuit after the source potential has varied by some given amount, said relay including a load switch having an operating coil, a control switch having its contacts connected to the coil of the load switch and to the source, and an operating coil for the control switch also connected to said source, the control switch having pickup and drop away values relatively close to one another and the load switch having pickup and drop away values substantially lower, respectively, whereby the load switch may function in lresponse to the pickup and drop away values ofV the control switch.

6. In combination, a source of electromotive force, a relay for changing the condition of an electrical circuit after the source potential has varied by some given amount, said relay comprising a load. switch of the mercury displacement type in which the intermittently immersed electrode has aform which inherently adapts the switch to high load, but eifects a relatively large span between the'pickup and drop away values of the switch. an operating coil for the load switch, a control switch having its contacts connected to the coil of the load switch and to the source'and being of a type which is'inherently capable of operating on arelatively small span between pickup kand drop away values, and an' operating eoilfor the control switch also connected to the source. l

7. In combination, a source of electromotiveforce tbatis subject to comparatively gradual rises and falls in potential and/or rapid fluctuations in voltage within rather vnarrow ranges of potential,l a mercury switch relay connected to said source and adapted to change the ,condition of an electrical circuit whenever the source po-` tential has exceeded yor fallen below predetermined maximum and minimum values, respectively, fora specified length of time, said relay, comprising a load switch of the slow make, slow break mercury displacement type, a coil for operating the load switch, a control switch having its contacts in series with the coil of the load switch, and an operating coil for the control switch connected to said source.

8. In combination, a source of electromotive force, a relay for changing the condition of an electrical circuit afterthe source potential has varied by some givenamount, said relay including a load switch, a control switch, and operating coils for each, and means for connecting the coil of the control switch to the source, and the coil of the load switch to the source but in series with the contacts of the control switch whereby the load switch coil is energized only when the control switch contacts are closed and the load switch though controlled by the same source which operates the control switch is characterized by positive oil and on action in its operation, said series connection operating to continuously maintain the load switch in its desired position until the source has varied by said given amount and then return the load switch to said position whenever the voltage returns to its normal value. i

9.1In combination, a source of electromotive force, a relay for changing the condition of an electrical circuit whenever the source has fallen below a specified voltage for a predetermined length of time, said relay including a load switch, a coil for operating the load-switch, a control switchA adapted to operate the load switch, an operating coil for the control switch connected to the source, and means for delaying the changingoi.' the condition oi the electrical circuit through the load switch until after the source has fallen below a specified voltage for a predetermined length "of time, said means including a time delay element associated with the load switch whose action begins when the voltage falls below the specied value and which immediately resets itself whenever the voltage rises above the pickup value ofthe control switch. i

10. In combination, a source of electromotive force, a relay for changing the condition of an electrical circuit after the source potential has varied by some given amount, said relay comfor the load switch, a control switch .having its contacts connected to the coil of theJoad switch and to the source and being of a type which is inherently capable of operating on a relatively small span between pickup and drop away values,

andan operating coil for the control switch also connected to the source.

` UNO C. HEDIN..

CARL H. LARSON. 

